Comprehensive evaluation of effective constituents in total alkaloids from Sophora alopecuroides L. and their joint action against aphids by laboratory toxicity and field efficacy

Alkaloids are the main constituents that contributed to the insecticidal activity of plant Sophora alopecuroides L. (Fabaceae). Using an acid extraction and alkali precipitation method, total alkaloids were extracted and then six alkaloids were isolated, which were identified as matrine, oxymatrine, aloperine, cytisine, sophocarpine and sophoridine. To characterize the aphicidal spectrum and joint action of these compounds, their contact toxicity and joint action against aphids were evaluated by bioassay and field trial. Results showed that all the test alkaloids had high and broad spectrum aphicidal activities, but the toxicities varied significantly among alkaloids with different aphid species. Based on contact toxicity, cytisine was the most active alkaloid among six monomers. In the meantime, it was confirmed that the combination of cytisine, aloperine, oxymatrine and sophocarpine showed the most significant synergistic effect against A. craccivora, with the poison ratio of 1.62. Furthermore, field trials on four aphid species also indicated that the quaternary alkaloids possessed a more significant efficacy than others, with the efficacy about 80% on the 7th day post application. Thus, both bioassay and field trial proved that the combination of the four monomers possesses strikingly aphicidal synergistic action. As environmental friendly natural products, S. alopecuroides alkaloids can serve as potential, broad spectrum aphid-control agents, and the four alkaloid monomers would be important quality parameters for development and application of pesticide products from S. alopecuroides alkaloids.